1. Field of the Invention
The present invention relates to a feedhorn, a radio wave receiving converter and an antenna, and particularly to a feedhorn having a dielectric antenna, a radio wave receiving converter and an antenna.
2. Description of the Background Art
An antenna for receiving radio waves of satellite broadcasting or the like has been known. A radio wave receiving converter is utilized in conjunction with the antenna. As a component of the radio wave receiving converter, a feedhom having a dielectric antenna connected to an open end of a waveguide has been known (see for example Japanese Patent Laying-Open No. 2001-217644).
Japanese Patent Laying-Open No. 2001-217644 discloses that a part of the dielectric antenna is press-fit within the internal periphery of the open end of the waveguide so as to connect and fix the dielectric antenna to the waveguide.
Regarding the feedhorn having the above-described structure, however, high dimensional precision of the internal periphery of the waveguide and the aforementioned part of the dielectric antenna must be maintained. Otherwise, it is impossible to ensure reliability of the connecting portion connecting the waveguide and the dielectric antenna to each other. Further, if a change in ambient temperature causes the dielectric antenna to thermally expand or thermally contract, the strength of the connecting portion connecting the waveguide and the dielectric antenna could change. In this case as well, the reliability of the connecting portion deteriorates. As a result, the converter including the feedhorn as well as the antenna including this converter could deteriorate in reliability. In order to avoid occurrence of such problems, the inventor of the present invention conducted studies on the approach of tightly attaching, to the dielectric antenna, a cover member placed to cover the dielectric antenna and thereby pressing to fix the dielectric antenna to the waveguide.
In this case, however, if the dielectric antenna is changed in shape, the shape of the cover member has to be changed as well. For example, if feedhorns are to be mounted respectively on two types of parabolic antennas that are different for example in angular aperture and FD ratio, two types of radiation patterns of the feedhorns are also necessary. Therefore, dielectric antennas of two different types in shape are necessary as well. Further, two types of cover members are also necessary. Consequently, an increased number of molds are required for manufacturing feedhorns, which is a factor of an increase in manufacturing cost of the feedhorn.